1. Field of the Invention
The present invention relates to multi-point-to-point communication system and communication apparatus capable of multi-point-to-point communication by connecting a plurality of communication terminals, and more particularly to a multi-point-to-point communication system, communication apparatus, communication method and storage medium containing program for indicating the communication method capable of smooth multi-point-to-point connection.
2. Related Background Art
With recent advancement of image compression coding technique and population of a high speed and high quality digital line as represented by ISDN, a recommendation for AV (audio visual) services was defined by the ITU-T Recommendations H.320, H.242 and H.221 Recommendations and various television conference system which are in accord with those Recommendations have been developed. Such television conference systems include a multi-point-to-point television conference system which allows the television conferences among three or more multi-points. In the ISDN, any user information may be stored in user information which may be added to a specific control signal in a D-channel (control channel) or a sub-address which may be added to a call setup message for transmission.
The multi-point-to-point television conference system includes a multi-point-to-point connection configuration which uses an MCU (multi-point-to-point conference control unit) and a multi-point-to-point connection configuration which does not use the MCU but connects the television conference terminals in ring or chain.
In the multi-point-to-point configuration which does not use the MCU, a multi-point-to-point connection list storing information of the television conference terminals participating in the multi-point-to-point television conference is transferred between adjacent television conference terminals, and based on the information of the received multi-point-to-point connection list, a destination television conference terminal is determined and in this manner the ring or chain shaped multi-point-to-point connection is configured. In the multi-point-to-point connection which does not use the MCU, adjacent television conference terminals are directly connected to configure the ring or chain shaped communication path. Thus, at least two B-channels (information channels) must be empty in order to set two adjacent television conference terminals and the communication path in each of the television conference terminals participating in the multi-point-to-point television conference.
FIG. 2 shows a connection configuration for connecting four-point television conference terminals in ring as an example of the multi-point-to-point connection which does not use the MCU.
In FIG. 2, numeral 200 denotes an ISDN basic interface for forming two B-channels for transferring user data and one D-channel for transferring control data, numeral 201 denotes a television conference terminal (hereinafter referred to as a control television conference terminal) which performs a quasi-MCU function to control the present multi-point-to-point television conference, numerals 202-204 denote television conference terminals (hereinafter referred to as participating television conference terminals) which participate in the present multi-point-to-point television conference and numeral 205 denotes one B-channel path of the ISDN basic interface 200 connecting the television conference terminals 201-204.
In conducting the ring-shaped multi-point-to-point connection as shown in FIG. 2, it is common that the control television conference terminal (typically a television conference terminal that calls the multi-point-to-point television conference) for controlling the multi-point-to-point connection is provided as shown by 201 in FIG. 2 and the control television conference terminal determines the connection configuration for connecting the other participating television conference terminals (which television terminal calls and connects to which television conference terminal).
FIG. 3 shows a sequence of a multi-point-to-point connection procedure (protocol) for the four points shown in FIG. 2.
In S300, call and connection are made from the control television conference terminal 201 of the multi-point-to-point television conference to the participating television conference terminal 202.
In S301, as connection process between the control television conference terminal 201 and the participating television conference terminal 202, a D-channel connection procedure (protocol), a synchronization establishment procedure (protocol) and a capability exchange procedure (protocol) are executed to establish a data transfer path (hereinafter referred to as a data path) which utilizes LSD (low speed data) of the H.221 frame between the control television conference terminal 201 and the participating television conference terminal 202.
In S302, a connection request including information on an address number of the participating television conference terminal 203 is informed from the control television conference terminal 201 to the participating television conference terminal 202 in order to additionally connect the participating television conference terminal 203.
In S303, the participating television terminal 202 receives the connection request of S302 and conducts call and connection to the participating television conference terminal 203.
In S304, as connection process between the participating television conference terminal 202 and the participating television conference terminal 203, the D-channel connection protocol, the synchronization establishment protocol and the capability exchange protocol are executed to establish a data path between the participating television conference terminal 202 and the participating television conference terminal 203.
In S305, the completion of the connection process between the participating television conference terminal 202 and the participating television conference terminal 203 is informed by the data path from the participating television conference terminal 202 to the control television conference terminal 201.
In S306, a connection request including information on the address number of the participating television conference terminal 204, etc. is informed over the data path from the control television conference terminal 201 to the participating television conference terminal 203 through the participating television conference terminal 202 in order to additionally connect the participating television conference terminal 204.
In S307, the participating television conference terminal 203 receives the connection request of S306 and calls the participating television conference terminal 204.
In S308, as the connection process between the participating television conference terminal 203 and the participating television conference terminal 204, the D-channel connection protocol, the synchronization establishment protocol and the capability exchange protocol are executed and a data path between the participating television conference terminal 203 and the participating television conference terminal 204 is established.
In S309, the completion of the connection process between the participating television conference terminal 203 and the participating television conference terminal 204 is informed over the data path from the participating television conference terminal 203 to the participating television conference terminal 201 through the participating television conference terminal 202.
In S310, a connection request including information on the address number of the television conference terminal 201 is informed over the data path from the control television conference terminal 201 to the participating television conference terminal 204 through the participating television conference terminals 202 and 203 in order to connect the participating television conference terminal 204 and the control television conference terminal 201.
In S310, the participating television conference terminal 204 receives the connection request of S310 and calls and connects the participating television conference terminal 201.
In S312, as the connection process between the participating television conference terminal 204 and the control television conference terminal 201, the D-channel protocol, the synchronization establishment protocol, the capability exchange protocol, etc. are executed and a data path between the participating television conference terminal 204 and the participating television conference terminal 201 is established.
By the above procedure, the multi-point-to-point connection process of the participating television conference terminals 201-204 is completed and the multi-point-to-point communication is ready.
In the example of the multi-point-to-point connection shown in FIGS. 2 and 3, it is assumed that all of the participating television conference terminals of the multi-point-to-point television conference can be multi-point-to-point connected (at least two B-channel are available). In FIGS. 2 and 3, if one of the participating television conference terminals 201-204 is in communication with a television conference terminal which is not related to the multi-point-to-point television conference, the normal multi-point-to-point connection protocol shown in FIG. 3 cannot be executed.
FIG. 4 shows an example in which the participating television conference terminal 203 is in communication with other television conference terminal 400 in the multi-point-to-point connection shown in FIG. 2.
FIG. 5 shows a sequence of multi-point-to-point connection protocol when a participating television conference terminal which cannot be multi-point-to-point connected as shown in FIG. 4 is included in the multi-point-to-point connection protocol.
In S500, the control television conference terminal 201 of the multi-point-to-point television conference calls and connects the participating television conference terminal 202.
In S501, as the connection process between the control television conference terminal 201 and the participating television conference terminal 202, the D-channel connection protocol, the synchronization establishment protocol, the capability exchange protocol, etc. are executed and a data path between the control television conference terminal 201 and the participating television conference terminal 202 is established.
In S502, a connection request including information on the address number of the participating television conference terminal 203 is informed over the data path from the control television conference terminal 201 to the participating television conference terminal 202 in order to additionally connect the participating television conference terminal 203.
In S503, the participating television conference terminal 202 receives the connection request of S502 and calls and connects the participating television conference terminal 203.
In S504, as the connection process between the participating television conference terminal 202 and the participating television conference terminal 203, the D-channel connection protocol, the synchronization establishment protocol, the capability exchange protocol, etc. are executed and a data path between the participating television conference terminal 202 and the participating television conference terminal 203 is established.
In S505, the completion of the connection process between the participating television conference terminal 202 and the participating television conference terminal 203 is communicated over the data path from the participating television conference terminal 202 to the participating television conference terminal 201.
In S506, a connection request including information on the address number of the participating television conference terminal 204 is communicated over the data path from the participating television conference terminal 201 to the participating television conference terminal 203 through the participating television conference terminal 202 in order to additionally connect the participating television conference terminal 204.
In S507, when one B-channel is busy communicating with the television conference terminal 400, the incapability of communication between the participating television conference terminals 203 and 204 is communicated over the data path from the participating television conference terminal 203 to participating television conference terminal 201 through participating television conference terminal 202.
In S508, the disconnection of the participating television conference terminal 203 which was not multi-point-to-point connected is informed over the data path from the control television conference terminal 201 to the participating television conference terminal 202.
In S509, the participating television conference terminal 202 receives the disconnection request of S508 and executes a disconnection protocol including the capability exchange protocol, etc. to disconnect the participating television conference terminal 203.
In S510, the participating television conference terminal 202 disconnects the participating television conference terminal 203.
In S511, the completion of the disconnection of the participating television conference terminal 203 is communicated over the data path from the participating television conference terminal 202 to the control television conference terminal 201.
In S512, a connection request including information on the address number, etc. of the participating television conference terminal 204 is communicated over the data path from the control television conference terminal 201 to the participating television conference terminal 202 in order to additionally connect the participating television conference terminal 204.
In S513, the participating television conference terminal 202 receives the connection request of S512 and calls and connects the participating television conference terminal 204.
In S514, as the connection process between the participating television conference terminal 202 and the participating television conference terminal 204, the D-channel connection protocol, the synchronization establishment protocol, the capability exchange protocol, etc. are executed and a data path between the participating television conference terminal 202 and the participating television conference terminal 204 are established.
In S515, the completion of the connection process between the participating television conference terminal 202 and the participating television conference terminal 204 is communicated over the data path from the participating television conference terminal 202 to the control television conference terminal 201.
In S516, a connection request including information on the address number, etc. of the control television conference terminal 201 is communicated over the data path from the control television conference terminal 201 to the participating television conference terminal 204 through the participating television conference terminal 202.
In S517, the participating television conference terminal 204 receives the connection request of S516 and calls and connects the control television conference terminal 201.
In S518, as the connection process between the participating television conference terminal 204 and the control television conference terminal 201, the D-channel connection protocol, the synchronization establishment protocol, the capability exchange protocol, etc. are executed and a data path between the participating television conference terminal 204 and the control television conference terminal 201 is established.
By the above procedure, the multi-point-to-point connection process of the television conference terminals 201, 202 and 204 is completed and the multi-point-to-point communication is ready.
In the prior art multi-point-to-point television conference system, as shown in FIG. 4, if a participating television conference terminal of the multi-point-to-point television conference is in communication with a television conference terminal which is not related to the multi-point-to-point television conference, the normal multi-point-to-point connection protocol as shown in FIG. 3 cannot be executed and a complex error recovery process as shown in FIG. 5 is needed. As a result:
1) since the charge to the television conference terminal having the B-channel is terminated during the process of starting the multi-point-to-point connection, additional charge is accrued which is not related to the actual multi-point-to-point television conference due to the time required to complete the multi-point-to-point connection; PA1 (2) extra charge also accrues because the B-channel is connected to a television conference terminal which is not multi-point-to-point connected; and PA1 (3) the user is required to wait during the time required to complete the multi-point-to-point connection.